This application claims the priority of Japanese Patent Application No. 3-101371 (UM) filed on Nov. 12, 1991 which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a camera provided with a light emitting device for active autofocusing control.
2. Description of the Related Art
In active autofocusing control in cameras, the subjective distance is measured by projecting a light beam from a light emitting device onto the object of photography and receiving the light reflected from the object by a light receiving device. FIG. 5 shows the arrangement on the front surface of a camera. As shown in FIG. 5, a finder 2 and a lens barrel 4 holding a lens 3 are disposed on the front surface of the camera 1, and a light emitting device (light emitting diode) 5 for emitting infrared light and a light receiving device (photodiode) 6 are arranged in a horizontal line.
FIGS. 6A and 6B show an arrangement for attaching the light emitting device 5 to a camera body 9 through an adapter frame 8. The light emitting device 5 is provided therein with a light emitting (diode) chip 5A, and a light shielding mask (light shielding member) 10 as a separate member is provided on the light emitting surface of the light emitting chip 5A except for an opening 10A. A photographing lens 11 is provided on the camera body 9. According to the light emitting device 5, it is possible to shield the light emitted from the light emitting chip 5A and scattered to the circumference by the light shielding mask 10 and to project a light beam having a predetermined intensity and a predetermined diameter onto the object. When the light projected onto the object and reflected therefrom is received by the light receiving device 6, the subject distance is measured and the autofocusing (AF) step number is output. In accordance with the information on the AF step number, the photographing lens 11 is driven, thereby focusing the lens 11 on the object.
However, in the conventional arrangement for attaching the light emitting device 5 to the camera body 9, since the light shielding mask 10 is attached to the light emitting surface of the light emitting device 5 and the light emitting device 5 is in turn attached to the adapter frame 8, attachment of the light emitting device 5 including the light shielding mask 10 is laborious, and it is difficult to accurately position the light beam which is formed at the opening 10A of the light shielding mask 10. In autofocusing control, since the subject distance is measured from the position at which the beam is received by the light receiving device 6, if the position at which the light beam is formed by the light emitting device 5 is inaccurate, an error is produced in measuring the subject distance.
FIGS. 3 and 4 show the state in which the subject distance is measured. As shown in FIG. 3, when beams are projected from the light emitting device 5 onto the objects at different distances P.sub.1, P.sub.2, the beams reflected from the objects are received by the light receiving device 6 through a light receiving lens 7. At this time, the light receiving device 6 receives the beam reflected from the object which is at a distance of P.sub.1 at a position P.sub.1, and the beam reflected from the object which is at a distance of P.sub.2 at a position P.sub.2 in the direction of the base length which connects the light emitting device 5 and the light receiving device 6. It is therefore possible to specify the subject distance from the position (center of gravity) at which the beam is received by the light receiving device 6. The AF step number which corresponds to the subject distance is allotted to the light receiving device 6 for the purpose of autofocusing control, for example, as shown in FIG. 4. The AF step number n is determined from the center 200 of gravity of the received beam 100. Consequently, if the position to which the light emitting device 5 projects a light beam shifts, the position at which the light receiving device 6 receives the beam also shifts. It is therefore important to set the position to which the light emitting device 5 projects a light beam, and it is necessary to accurately arrange the light emitting device 5 on the adapter frame 8 and the light shielding mask 10 on the light emitting device 5.
However, since the light shielding mask 10 is a separate body in the conventional arrangement, it is necessary to maintain the accuracy with which the light emitting device 5 is attached to the adapter frame 8 and the accuracy with which the light shielding mask 10 is attached to the light emitting device 5 separately from each other, which leads to a rise in the cost.